The present invention relates to a high-purity copper or high-purity copper alloy sputtering target, a process for manufacturing the foregoing sputtering target, and a high-purity copper or high-purity copper alloy sputtered film. Incidentally, “%” and “ppm” as used herein respectively represent “mass %” and “mass ppm”. Moreover, “purity” represents the purity excluding C, O, N and H as gas components.
Conventionally, if the aim is to produce a high-purity copper or high-purity copper alloy target, emphasis was primarily placed on eliminating metal elements and nonmetal elements, which are recognized as impurities, excluding copper or alloy components, and limiting gas components to a constant amount of several ppm to several hundred ppm.
Thus, trace amounts of inclusions that existed in the high-purity copper or high-purity copper alloy target were not acknowledged as a problem, and no consideration was given for eliminating or reducing the same. Moreover, even in cases where gas components are limited as much as possible, there was no concern with respect to the existence form of the inclusions arising therefrom.
Nevertheless, if there are nonmetal inclusions in the high-purity copper or high-purity copper alloy target, even if they are minute and in trace amounts, protrusions (nodules) would arise on the target surface during the process of forming a thin film by way of sputtering, and particles would arise due to the rupture or the like of the protrusions (nodules) caused by an abnormal discharge. Generation of the foregoing particles causes the percent defective of the semiconductor device to deteriorate.
It was conventionally thought that the other causes had a greater influence on the generation of the foregoing particles, and the recognition of minute and trace amounts of inclusions existing in the high-purity copper or high-purity copper alloy target as the cause was insufficient.
Nevertheless, as the conventionally recognized sources of particles become clarified and subsequently removed, the new recognition is that other sources of particles exist and that it is not possible to realize high quality deposition unless they are removed.
To put it differently, existing sputtering targets for forming copper wiring for use in semiconductors are based on the foregoing sophisticated technology level.
Since the deposition technology of copper wirings for use in semiconductors is well known technology, the principle of deposition based on the sputtering method is briefly explained below.
The sputtering method is to form a film on a substrate by utilizing the phenomenon where atoms configuring the target are discharged into space and accumulated on the opposing substrate based on the momentum exchange that occurs when the accelerated charged particles collide with the target surface.
The sputtering target is usually in the shape of a discoid or rectangular plate, and is used as the sputter source for forming, on the substrate, an electrode, gate, element, insulating film, protective film and the like for various semiconductor devices by way of sputtering.
Generally speaking, as the sputtering target, an aluminum and aluminum alloy target, a copper and copper alloy target, a high-melting-point metal and alloy target, a metal silicide target and the like are used.
Among the foregoing targets, an important target is a copper and copper alloy target that is used in forming a copper wiring as an alternative of a conventional aluminum wiring.
Meanwhile, during the deposition based on sputtering, protrusions having a size of several μm to several mm, referred to as nodules, sometimes arise on the eroded portion of the sputtering target. There is a problem in that such nodules will burst as a result of colliding with the charged particles during the sputtering process, and thereby cause the generation of particles (cluster-state coarse fragments) on the substrate.
The generation of particles will increase in proportion to the amount of nodules on the eroded surface of the target, and a major issue is to prevent the generation of nodules in order to reduce the problematic particles.
Under the recent circumstances where LSI semiconductor devices are subject to higher integration and the linewidth thereof becomes miniaturized to 0.25 μm or less, the generation of particles caused by the foregoing nodules is now being considered a major problem.
Specifically, particles directly adhere to the thin film that is formed on the substrate, or once adhere to and accumulate on the peripheral wall or component of the sputtering device and thereafter flake off and once again adhere to the thin film; and it causes problems such as the disconnection or short circuit of the wiring. The generation of particles is becoming a major problem pursuant to the advancement of higher integration and miniaturization of the electronic device circuit as described above.
As described above, the conventionally recognized sources of particles are being clarified and many have been removed, but the current situation is that it is still insufficient. Unless these other sources of particles are removed, it is not possible to achieve high quality deposition.
Conventional technologies are now introduced. Nevertheless, the following conventional technologies have no concern regarding the shape and influence of the minute and trace amounts of inclusions existing in the high-purity copper, and do not provide any kind of specific solution therefor.
Patent Document 1 describes cleaning electrolyte based on solvent extraction.
Patent Document 2 describes eliminating Sb and Bi with chelate resin.
Patent Document 3 describes adding a diaphragm and glue in copper electrolysis to smooth the electrolyzed surface, and thereby reducing the uptake of impurities.
Patent Document 4 describes bringing anolite into contact with activated carbon in copper electrolysis to eliminate glue.
Patent Document 5 describes performing electrolysis once again in copper electrolysis.
Patent Document 6 describes smoothing the electrode surface based on periodic reverse-current electrolysis in copper electrolysis to prevent the inclusion of suspended solids and electrolyte.
Patent Document 7 describes adding a macromolecular additive to improve the surface condition and using electrolyte containing urea in copper electrolysis to produce high-purity copper with a low silver and sulfur content.
Patent Document 8 describes that the three metallurgical characteristics of a sputtering target affecting the performance of the target are: the uniformity of the material (no precipitate, void, inclusion and other defects); crystal grain size (finer crystal grain size is generally more preferable than coarse crystal grain size); and texture (texture relates to the strength of a specific crystallographic orientation, that is, a “weak” texture includes substantially random distribution of the crystallographic orientation, and a “strong” texture includes a preferential crystallographic orientation in the distribution of the crystallographic orientation). Patent Document 8 further describes that it is generally necessary to reduce defects such as inclusions in the target.
Patent Document 9 discloses a titanium sputtering target in which the number of inclusions of 1 μm or more existing at the crystal grain boundary of titanium configuring the target is 100 inclusions or less per 1 cm2 of the target plane. Patent Document 9 additionally describes that the inclusions existing at the crystal grain boundary of titanium are a composite compound based on a combination of one or more types among oxides, nitrides, carbides, sulfides, and hydrides of metal components of titanium or iron, nickel, chromium, aluminum, silicon, tungsten and molybdenum, and that the oxides can be decomposed by heat treatment.
Patent Document 10 and Patent Document 11 describe that the number of inclusions in an aluminum or aluminum alloy target is reduced to be 40 inclusions/cm2 or less per unit area; splashes can be reduced by bringing the maximum length of the inclusions to 20 μm or less; to reduce the inclusions in the sputtering target is particularly important in order to inhibit the generation of particles and splashes; and inclusions are reduced by filtering molten metal with a ceramic filter.
Patent Document 12 discloses a high-purity copper or copper alloy sputtering target, wherein the target has an oxygen content of 100 ppm or less, a carbon content of 150 ppm or less, a nitrogen content of 50 ppm or less, and a sulfur content of 200 ppm or less, or the number of indications having a flat-bottomed hole diameter of 0.5 mm or more is 0.014 indications/cm2 or less on an ultrasonic inspection performed from the target surface; and a process for manufacturing a high-purity copper or copper alloy sputtering target having an oxygen content of 100 ppm or less, a carbon content of 150 ppm or less, a nitrogen content of 50 ppm or less, and a sulfur content of 200 ppm or less, wherein used is a high-purity copper or copper alloy ingot obtained by melting and casting based on electron beam melting or vacuum induction skull melting. However, inclusions large enough to be detected on the ultrasonic inspection are not observed in current high-purity copper targets.
Patent Document 13 describes that oxygen, nitrogen and carbon as gas components contained in the copper alloy sputtering target form inclusions at the crystal grain boundary and cause the generation of particles, and that it is desirable to reduce such gas components as much as possible since they cause the unexpected generation of particles during the sputter life. Patent Document 13 also describes that unavoidable impurities excluding gas components are reduced to 10 wtppm or less.
[Patent Document 1]
Japanese Laid-Open Patent Publication No. H11-106842
[Patent Document 2]
Japanese Laid-Open Patent Publication No. 2000-107596
[Patent Document 3]
Japanese Laid-Open Patent Publication No. S63-297583
[Patent Document 4]
Japanese Laid-Open Patent Publication No. S64-55394
[Patent Document 5]
Japanese Laid-Open Patent Publication No. H1-152291
[Patent Document 6]
Japanese Laid-Open Patent Publication No. S64-8289
[Patent Document 7]
Japanese Laid-Open Patent Publication No. 2005-307343
[Patent Document 8]
Japanese Laid-Open Patent Publication No. 2004-513228
[Patent Document 9]
Japanese Laid-Open Patent Publication No. H5-214519
[Patent Document 10]
Japanese Laid-Open Patent Publication No. H9-25564
[Patent Document 11]
Japanese Laid-Open Patent Publication No. H11-315373
[Patent Document 12]
Japanese Laid-Open Patent Publication No. 2000-239836
[Patent Document 13]
WO2004/083482